This invention relates to a resinous composition for friction materials, and especially to resinous compositions for non-asbestos type clutch facings. This composition provides the desired flexibility to the base materials, provides compatability with base materials and provides superior friction characteristics for such applications.
The clutch facing for automobiles and other machines is composed of a base material of asbestos, a binder of thermosetting resin, and organic and inorganic additives. The thermosetting resin used as the binder is an unmodified phenolic resin, or a cashew-modified, oil-modified, or melamine-modified phenolic resin. The melamine-modified phenolic resin is preferred because of its stable friction characteristics.
Recently, there has arisen a demand for improved friction characteristics as the design for improved clutch facing has become more critical. On the other hand, the production of cancer by asbestos has become a social issue. Under these conditions, non-asbestos clutch facing has come into general use. The clutch facing of this type is made of glass fiber as the base material. As compared with the asbestos base material, glass fiber is poor in flexibility and wettability by resins. These disadvantages are amplified where the binder is a conventional melamine-modified phenolic resin. Although flexibility is improved by the use of cashew-modified, oil-modified, or rubber-modified phenolic resin, they lower the coefficient of friction of the resulting clutch facing. Accordingly, there has been a demand for a binder of thermosetting resin which imparts flexibility to the base material, is miscible with the base material, and provides superior friction characteristics.
In order to overcome the above-mentioned disadvantages, the inventors conducted a series of research programs, which led to the findings that a phenolic resin modified with a triazine resin compound and further with a liquid rubber imparts flexibility to the base material, is highly miscible with the base material, and provides superior friction characteristics.